It is known from U.S. Pat. Nos. 3,850,892 and 3,880,818 to make soft lenses by esterifying acrylic-type polymers, either by direct esterification in which an alcohol is reacted with the pendant carboxyl groups in the polymer, or by indirect esterification in which acid halide is reacted with the pendant carboxyl groups in the polymer, and also by transesterification in which an alcohol is reacted with pendant alkyl carboxylate groups in the polymer to obtain higher alkyl carboxylate groups.
One problem heretofore associated with such lenses is that the direct esterification method as set forth in the aforementioned patents produces lenses which crumble easily or have poor mechanical strength. Moreover, these lenses made by the direct esterification method according to the prior art are generally opaque or become opaque upon exposure to an aqueous environment. Such lenses are generally unsuitable for use as contact lenses or intraocular lenses.
Still another problem with the prior art method of making lenses of esterified acrylic-type polymers is that higher molecular weight alcohols, which are desirable from the standpoint of their ability to soften the lens material, cannot generally be substantially removed by evaporation.
To make intraocular lenses from a process incorporating the method of the aforementioned patents, there has heretofore been no method of which Applicants are aware to securely attach loops, or haptics, to the lenses without damaging the lenses or the haptics. For example, in one heretofore known method of heat stake welding, a haptic made of a material such as polypropylene or polymethylmethacrylate is inserted into a peripheral bore formed in the lens and welded to the lens by inserting hot filaments transversely into the lens material adjacent the peripheral bore. When the heat stake welding procedure is used with lenses made of the soft esterified acrylic-type polymer, the loops are not generally welded adequately in place, the soft lens material is in general deformed, and quite frequently a hole is formed through the lens in the principal area of the heat stake weld.
The present invention provides a method for making soft contact or intraocular lenses which avoids the above deficiencies in the prior art.